Disposable containers coated with a latex coating

ABSTRACT

A molded thermoplastic container e.g. cup, bowl made from expandable thermoplastic particles e.g. expandable polystyrene, has a latex coating, e.g. latex of methyl methacrylate and styrene copolymer, latex of methyl acrylate and styrene copolymer, latex of acrylic acid and styrene copolymer, and latex of butadiene and styrene copolymer, applied to at least its inner surface via dipping, brushing or spraying processes for improved leakage and/or stain resistance and/or storage longevity. The coating may be applied to the outer surface of the container for leak resistance and printing purposes. A related method for forming the container, an article of manufacture, and an improved method for storing liquid and food substances are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to disposable containers. More particularly, the present invention relates to molded foam containers that are made from thermoplastic particles, e.g. expandable polystyrene particles (EPS), and that are coated with a latex coating. The containers are used to retain liquids, e.g. coffee or foods containing oil and/or fatty components, e.g. precooked fat-containing foods, e.g. instant noodles, soups, fried chicken, sauces, and the like. The invention also relates to a method for forming a container, an article of manufacture, and an improved method for storing liquid and food substances.

2. Background Art

The manufacture of molded foam containers, e.g. cups, bowls, etc. from expanded thermoplastic particles is well known. The most commonly used thermoplastic particles are expandable polystyrene (EPS) particles.

Typically, polystyrene beads are impregnated with hydrocarbon, e.g. pentane as a blowing agent that boils below the softening point of the polystyrene and causes the beads to expand when heated.

The formation of molded containers from impregnated polystyrene beads is generally done in two steps. First, the impregnated beads are pre-expanded to a density of from about 2 to 12 pounds per cubic foot. Second, the pre-expanded beads are heated in a closed mold to further expand the pre-expanded beads to form a fused article having the shape of the mold.

The expandable polystyrene particles used to make foam containers are generally prepared by an aqueous suspension polymerization process, which results in beads that can be screened to relatively precise bead sizes. Typically, the raw bead diameters for making containers, such as cups, range from about 0.008 to about 0.02 inch. It has been known to produce cups from beads having a diameter of about 0.03 inches.

In spite of careful bead size control, one problem that continues to plague the container industry is that after a period of time the containers, especially those made from EPS particles, have a tendency to leak. That is, liquids, especially hot liquids, e.g. coffee, water, oil and/or fat, permeate around the fused polystyrene beads and leak onto the outer surface of the container. Generally, this results in an unsafe condition for the person holding the container and/or results in stains appearing on the outer surface of the container. It is known that leakage resistance is dependent on temperature. That is, hot liquid and food substances tend to penetrate around the fused beads faster than cold substances.

Several approaches have evolved over the years in an attempt to reduce leakage in containers that retain cold and hot liquids and/or pre-cooked foods.

Amberg et al., U.S. Pat. No. 4,036,675 discloses a container made from foamed plastic material, preferably foamed polystyrene, which is lined on one or both sides with unoriented polyolefin film, preferably polypropylene. The film is secured to the foamed plastic base material using as a heat-sensitive adhesive a vinylic polymer or polyamide resin. The film is coated with a wet adhesive and dried before laminating the film to the foam material. Laminating is done by heating the foam material to 250-275° F., preheating the coated film to 100-180° F., and pressing the coated film surface against the heated foam for 10 to 15 seconds by using a cold platen or roller.

Sonnenberg U.S. Pat. Nos. 4,703,065 and 4,720,429 disclose thermoplastic polymer foam cups for retaining coffee that are molded from thermoplastic polymer particles whose surfaces are coated with a fluorosurfactant before molding.

Sonnenberg U.S. Pat. No. 4,785,022 discloses a method for enhancing the coffee retention of molded foam cups, which involves coating the expandable polystyrene particles with various rubber polymers and copolymers. The rubber can be polybutene, polyisobutylene, isobutylene-butene copolymer and butene-ethylene copolymer.

Arch, et al. U.S. Pat. No. 4,798,749 approaches the problem of coffee leakage by replacing conventional blowing agents such as butanes, n-pentane, hexanes, and the halogenated hydrocarbons with isopentane in the expandable styrene polymer particles.

Ikeda, et al., U.S. Pat. No. 4,698,367 discloses expandable thermoplastic resin particles in which the thermoplastic resin, composed of fluorinated vinyl polymer and hydrophilic vinyl polymer, covers or is included on the surface or in the surface layer of the expandable thermoplastic particle. The resin particles are useful for producing package containers for oily or fatty foods.

Sakoda et al., U.S. Pat. No. 6,277,491 B1 is directed to preventing oil from penetrating into a molded container made from expandable thermoplastic resin beads. The resin beads are coated or incorporated with a fluorine-containing block copolymer comprising a fluorine-containing vinyl-type polymer segment derived from a fluorine-containing vinyl-type monomer and a lipophilic vinyl-type polymer segment derived from a lipophilic vinyl-type monomer.

The above prior art containers are addressed to polystyrene containers, such as cups or bowls. The following patents pertain to paper cups that are either spray coated or that contain a thermoplastic resin film either for heat insulating purposes or for producing a high impermeability to liquids.

For example, Suzuki et al., U.S. Pat. No. 4,206,249 discloses a process for producing a paper container having a high impermeability to liquids which involves spray coating a polymerizable solution containing a pre-polymer onto a wall surface of the paper container and irradiating the coated wall with ultraviolet light to set the pre-polymer onto the wall surface thereof. This forms a coating that is impermeable to liquids, such as water, milk, soft drinks, oils, etc. This patent teaches in column 2, lines 45-62, a method in which the interior wall surface of the container is lined with a thermoplastic film. The thermoplastic film is first laminated onto a blank and the blank is formed into a container.

Iioka, U.S. Pat. No. 4,435,344 discloses a heat-insulating paper container where the outer and inner surfaces are extrusion coated or laminated with a thermoplastic synthetic resin film. The resin film is converted into a foamed layer on the paper substrate and the container is formed. The result is a container with good thermo-insulation properties. This film preferably is polyethylene and as taught in column 3, lines 50-55, this resin film can be polypropylene, polyvinyl chloride, polystyrene, polyester, nylon and the like.

Iioka et al., U.S. Pat. No. 5,490,631 discloses a heat insulating paper container comprising a body member wherein a thick foamed heat insulating layer made of a thermoplastic synthetic resin film is formed in the printed area of the outer surface and a less thick foamed heat-insulating layer that can be made of the same thermoplastic synthetic resin film is formed in the non-printed area of the outer surface. The thermoplastic synthetic resin film is typically polyethylene.

Breining, et al., U.S. Pat. No. 6,416,829 B2 discloses a heat insulating paper cup where the body member is coated on its outside surface with a foamed low density polyethylene, and on its inside surface with an unfoamed modified low density polyethylene.

None of these prior art containers pertain to thermoplastic containers that are coated with a latex coating and are used to retain and/or store liquid and food substances, such as coffee, soups, stews, pre-cooked foods and the like.

SUMMARY OF THE INVENTION

The invention has met the above need. A thermoplastic container is molded from expandable thermoplastic particles and a latex coating is applied to a portion of at least one of the inner and outer surfaces of the container; preferably to the inner surface; and more preferably to both the inner and outer surfaces. The container is relatively impenetrable thereby substantially reducing or eliminating leakage, and therefore, stains from forming on the surfaces of the container.

The latex coating, if applied to the outer surface of the container can also be used for labeling and/or printing purposes.

The latex coating may be selected from the group consisting of latex of methyl methacrylate and styrene copolymer, latex of methyl acrylate and styrene copolymer, latex of acrylic acid and styrene copolymer, and latex of butadiene and styrene copolymer.

The thickness of the coating may range from about 0.10 mils (0.27 mg dry coating weight per square centimeter cup surface) to about 5.0 mils (13.4 mg dry coating weight per square centimeter cup surface), and preferably may be about 0.9 mils (about 0.25 mg dry coating weight per square centimeter cup surface). The coating may be applied to a portion of or to the entire inner and/or outer surface of the container. In an embodiment of the invention, the coating is applied substantially to the entire inner and/or outer surface of the container.

The latex coating is applied to the containers surfaces via a brushing process, a dipping process, or a spraying process, e.g. via an airless spraying device or devices.

The container is made from expandable thermoplastic resin beads, and in some embodiments, this expandable thermoplastic resin is expandable polystyrene (EPS).

Some embodiments of the invention involve a molded thermoplastic container that exhibits improved resistance to leakage and/or stain and improved insulation properties.

Some embodiments of the invention involve a latex coating that is applied to the inner and/or outer surface of a molded thermoplastic container.

Other embodiments of the invention involve a method for applying a latex coating to the surfaces of a molded thermoplastic container.

And still other embodiments involve an article of manufacture comprising a molded thermoplastic container that is coated with a latex coating and that contains a liquid or food substance, and which container has improved storage longevity, improved stain resistance, and/or improved leakage resistance.

These and other aspects of the invention will be more fully appreciated and understood from the following description and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In the invention, containers, e.g., cups, bowls, and the like are molded from expandable thermoplastic particles. The expandable thermoplastic particles are made from any suitable thermoplastic homopolymer or copolymer.

Particularly suitable for use are homopolymers derived from vinyl aromatic monomers including styrene, isopropylstyrene, alpha-methylstyrene, nuclear methylstyrenes, chlorostyrene, tert-butylstyrene, and the like, as well as copolymers prepared by the copolymerization of at least one vinyl aromatic monomer with monomers such as divinylbenzene, butadiene, alkyl methacrylates, alkyl acrylates, acrylonitrile, and maleic anhydride, wherein the vinyl aromatic monomer is present in at least 50% by weight of the copolymer.

Styrenic polymers are preferred, particularly polystyrene. However, other suitable polymers may be used, such as polyolefins (e.g. polyethylene, polypropylene), and polycarbonates, polyphenylene oxides, and mixtures thereof.

Preferably, the expandable thermoplastic particles are expandable polystyrene (EPS) particles. The particles can be in the form of beads, granules, or other particles convenient for expansion and molding operations. Particles polymerized in an aqueous suspension process are essentially spherical and are preferred for molding the foam container of the invention. The particles are screened so that their diameter ranges from about 0.008 to about 0.02 inch.

The expandable thermoplastic particles are impregnated with a suitable blowing agent using any conventional method. For example, the impregnation can be achieved by adding the blowing agent to the aqueous suspension during the polymerization of the polymer, or alternatively by re-suspending the polymer particles in an aqueous medium and then incorporating the blowing agent as taught in U.S. Pat. No. 2,983,692 to D. Alelio.

Any gaseous material or material which will produce gases on heating can be used as the blowing agent. Conventional blowing agents include aliphatic hydrocarbons containing 4 to 6 carbon atoms in the molecule, such as butanes, pentanes, hexanes, and the halogenated hydrocarbons, e.g. CFC's and HCFC'S, which boil at a temperature below the softening point of the chosen polymer. Mixtures of the aliphatic hydrocarbons blowing agents can also be used.

Alternatively, water can be blended with these aliphatic hydrocarbons blowing agents or water can be used as the sole blowing agent as taught in U.S. Pat. Nos. 6,127,439; 6,160,027; and 6,242,540 assigned to NOVA Chemicals (International) S.A. In the aforesaid patents, water-retaining agents are used. The weight percentage of water for use as the blowing agent can range from 1 to 20%. The teachings of U.S. Pat. Nos. 6,127,439, 6,160,027 and 6,242,540 in their entirety are incorporated herein by reference.

The impregnated thermoplastic particles are generally pre-expanded to a density of from about 2 to about 12 pounds per cubic foot. The pre-expansion step is conventionally carried out by heating the impregnated beads via any conventional heating medium, such as steam, hot air, hot water, or radiant heat. One generally accepted method for pre-expanding impregnated thermoplastic particles is taught in U.S. Pat. No. 3,023,175 to Rodman.

The impregnated thermoplastic particles can be foamed cellular polymer particles as taught in Arch et al. U.S. patent application Ser. No. 10/021,716 assigned to NOVA Chemicals Inc, the teachings of which in their entirety are incorporated herein by reference. The foamed cellular particles are preferably polystyrene that are pre-expanded to a density of from about 12.5 to about 34.3 pounds per cubic foot, and that contain a volatile blowing agent level less than 6.0 weight percent, preferably from about 2.0 wt % to about 5.0 wt %, and more preferably ranging from about 2.5 wt % to about 3.5 wt % based on the weight of the polymer.

In a conventional manner, the pre-expanded particles (“pre-puff”) are heated in a closed mold to further expand the particles and to form the foam molded container of the invention.

In general, the latex coating suitable for use in the invention is of the type that will not be detrimental to the thermoplastic particles forming the container. That is, the latex coating of the invention will be devoid of any chemicals that tend to dissolve or react with the thermoplastic particles, particularly polystyrene particles. For example, most solvent-based polymeric coatings would not be feasible in the invention.

“Latex” can be defined as a colloidal dispersion of polymer particles in an aqueous medium, such as water. The phase ratio (polymer phase to aqueous phase) may range from 40:60 to 60:40 by weight. In the latex coating industry, a more common term is “solids content”. “Solids content” as used herein refers to the dry matter that comprises the polymer, emulsifiers, inorganic salts, etc. in the latex coating. A typical range for the solids content is between 40 and 60 percent weight. This measurement is derived by drying a latex coating sample to a constant mass at a temperature between 100 and 140° C. The solids content is then expressed as the percentage ratio of the dry matter to the total mass of the sample.

The latex used in the invention may contain surfactants and/or other minor components. The surfactant, which generally is used for stability purposes, may be any of the commonly known surfactants used in latex coatings such as sodium octyl sulfonate, sodium decyl sulfonate, sodium dodecyl sulfonate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium dodecyl sulfate, branched sodium alkyl sulfate, sodium dodecyl ethoxylate (2EO ), dodecyl alcohol ethoxylate (5EO), dodecyl alcohol ethoxylate (7EO), dodecyl alcohol ethoxylate (8EO), etc.

A particularly suitable polymer of the latex coating of the invention may be a monomer selected from the group consisting of butadiene, n-butyl acrylate, i-butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, octyl acrylate, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl pivalate, vinyl neo-decanoate, acrylonitrile, methyl acrylonitrile, acrylamide, styrene, α-methyl styrene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate; or the polymer may be selected from the group consisting of a homopolymer or the copolymer of two or more of the above monomers or the copolymer of two or more of the above monomers with the following functional monomers including acrylic acid, methacrylic acid, itaconic acid, fumaric acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, acrylamide, dimethyl meta-isopropenyl benzyl isocyanate, N-methylolacrylamide, N-methylol methacrylamide, N-(iso-butoxymethyl)acrylamide, glycidyl acrylate, glycidyl methacrylate, sodium styrene sulfonate.

The latex coating may be comprised of a polymer selected from the group consisting of acrylate, ethyl acrylate, methyl methacrylate, methacrylate, acrylic acid, methacrylic acid, monomers or the copolymers of these monomers combined with vinyl acetate or styrene.

Preferred latex coatings are latex of methyl methacrylate and styrene copolymer, latex of methyl acrylate and styrene copolymer, latex of acrylic acid and styrene copolymer, and latex of butadiene and styrene copolymer.

The molecular weight for the latex coating may range from about 100 to about 1 million units (500 to about 200 million g/mol). The molecular polydispersity for the latex coating may be defined as ranging from very narrow to very broad, i.e. from about 1.0 to about 20.

The thermoplastic container may be a polystyrene cup that is fabricated by a conventional cup-forming machine that has an inner shell and an outer shell. A conventional cup-forming machine is Cup Production MODEL 6-VLC-125 machine, made by Autonational B.V. or is MODEL M10 cup machine, made by Master Machine & Tool Co.

In the invention, after the container is formed, the latex coating is applied to a portion of at least one of the inner and outer surfaces, preferably, the inner surface, and more preferably, both the inner and outer surfaces. Preferably, the latex coating is applied to substantially the entire inner and/or outer surface.

The latex coating may be applied to the surface or surfaces of the container via any suitable process, including a dipping process, a brushing process, or a spraying process via any suitable means. A spraying process may be preferred from both an economic and production standpoint.

The type of latex coating particularly suitable for the invention is comprised of polymers in solid particulate form and water. The initial solids content of the polymer may be about 48% to about 50% by weight, which can be adjusted to change the viscosity so that the process equipment, such as the spraying system, can adequately handle the application of the coating onto the container.

The solids content of the latex prior to being applied to the container's surface generally will depend on the process being used to apply the latex to the container. For example, if a spraying process or a brushing process is used, preferably the solid contents will range from about 40% to about 47% by weight, based on the weight of the latex. If a dipping process is used, preferably the solid contents will range from about 8% to about 20% by weight.

After the latex is applied to the surface or surfaces of the container, the container may then be carried via a transport belt to a drying chamber or oven. The drying oven may be a conventional oven and the heating medium may be hot air, radiant heat, or heat plus vacuum. Preferably, the heating medium is hot air. A typical drying oven is obtained from Blue M Electric Company, Blue Island, Ill. The drying time is dependent on the drying temperature, the solids content of the coating, and the coating thickness. For example if the coating is 1.5 mils, the drying temperature will be about 90° C. with a drying time of about 60 seconds. Typically, the drying temperature will range from about 50° C. to about 100° C. and the drying time will range from about 5 seconds to about 3000 seconds for coatings with a solids content ranging from about 8% to about 47% by weight.

As stated herein, the thickness of the latex coating on the surface or surfaces of the container may range from about 0.10 mils (0.27 mg dry coating weight per square centimeter cup surface) to about 5.0 mils (13.4 mg dry coating weight per square centimeter cup surface), and preferably may be about 0.9 mils (0.25 mg dry coating weight per square centimeter cup surface). This coating thickness may extend on a portion of or substantially on the entire inner and/or outer surface of the container.

In a preferred embodiment of the invention, the latex is applied to the container via a spraying process. The production rate for a single spraying device for spray coating the latex onto the inner surface of a 16-ounce cup may range from about 50 to about 600 cups per minute. It is apparent that several spraying devices can be used to accommodate the desired production rate of the cups.

A spraying device that may be useful in the invention is an airless spraying device available from Nordson Corporation. An example of a spraying device provided by Nordson Corporation is disclosed in the aforesaid Suzuki et al., U.S. Pat. No. 4,206,249. In this instance, it is preferable that the airless spraying device applies the latex at room temperature instead of at the elevated temperatures taught in U.S. Pat. No. 4,206,249. It is understood that minor modifications can be made to the spraying device of the '249 patent when spraying the latex coating of the invention.

The coating rate can be defined as “the dry weight of the coating sprayed onto the unit surface area of the container”. As stated herein, the coating rate may range from about 0.27 milligrams to about 13.4 milligrams dry coating weight per square centimeter cup surface.

The latex is applied to a portion of or substantially onto at least one of the inner and outer surfaces of the container to form a coating; preferably to the inner surface; and more preferably to both inner and outer surfaces.

The latex coating may be applied to the outer surface for leakage resistance purposes and/or for labeling and printing purposes. It is to be understood that the container has both a sidewall and a bottom section and that the “inner surface” and the “outer surface” generally will refer to both the sidewall and bottom section of the container.

The invention is further illustrated, but not limited by, the following examples.

EXAMPLES Example 1

This example illustrates the preparation of latex coated containers. Expandable polystyrene cup beads (DYLITE® beads from NOVA Chemicals, Inc., which comprise polystyrene and pentane) were blended with zinc stearate and pre-expanded in an 11-gallon (about 1.5 cubic foot) Rodman Steam pre-expander (Artisan Industries Inc.) at atmospheric pressure. The pre-expansion was operated batch wise. 3.5 pounds of cup beads having a diameter distribution of about 0.008 inches to about 0.02 inches were used to make pre-puff with a density of about 3.5 pounds per cubic foot. The newly prepared pre-puff was air dried for 5 minutes to remove the moisture and aged for about 4 hours before molding.

Sixteen-ounce cups were molded from the aged pre-puff beads. The steam header pressure was 80 pounds per square inch and the total cycle time was in the range of 6 to 15 seconds. The molded foam cups were allowed to age overnight.

Latex (Roymal 45526 product manufactured and marketed by Roymal Incorporated, which is a latex of methyl acrylate, acrylic acid, and styrene copolymer), was sprayed onto the inner surface, i.e. both the sidewall and the bottom, of the cups at a coating rate of 1.7 to 4.3 mg dry coating weight per square centimeter cup surface, using an airless spray device manufactured and sold by the Nordson Corporation. For this latex product, the ratio of styrene to methyl acrylate may range from about 5:95 percent weight to about 95:5 percent weight based on the weight of the polymer segments, and the acrylic acid may range from about 0 to 10% by weight in the total polymer weight. The latex contained 48% by weight solids.

Prior to applying the latex to the inner surface, the latex was diluted with de-ionized water to produce a latex containing 46% by weight solids.

The coated cups were then dried in an oven using a combination of hot air circulation and radiant heat at 90° C. for 1 minute. The coated cups were stored overnight before being tested.

The coated cups were tested by the following method: Spicy oil at room temperature was poured into each container to fill the cup up to about 80% of its capacity. The outer surface of each container was observed for oil stains and leakage every 10 minutes for the first 1.5 hours, every 30 minutes in the time frame from 1.5 hours to 6 hours, and, then, every hour thereafter for a total of 48 hours.

The average time to failure (ATF) for each cup group sampling was calculated by adding the time to failure for each container, and dividing the total time to failure by the number of containers tested. Typically, ten cups in each group were tested. A maximum ATF value of 48 hours means that none of the cups in that group exhibited any stain or leakage. A minimum ATF value of 0.17 hours means that all of the cups in that group failed within the first 10 minutes.

The results for the oil retention (ATF) are shown in Table 1. As indicated, the cups with the latex coating had an increased ATF compared to the cups without the latex coating (control). TABLE 1 Coating rate (mg/cm²) 0 1.7 2.5 3.8 4.3 ATF (hour) 0.83 38.9 48 48 48 Remark Control

Example 2

The EPS cups were 6 ounce cups. The oil retention test (ATF) for these EPS cups having a pre-puff density of 3.5 pounds per cubic foot was performed in a manner similar to that for Example 1.

The type of latex coating was the same as that used in Example 1. The coating was first diluted with water to produce coatings with varying solids content. The molded foam cups were coated via a dip coating process with the diluted latex so that both the inner and the outer surfaces of the cups were coated. The coated cups were dried at room temperature overnight before being tested. The results are shown in Table 2.

The cups with the latex coating have an increased ATF compared to those cups without the latex coating (control). TABLE 2 Coating Thickness 6.0μ 9.0μ 12.0μ Solid — 8.08 12.13 16.17 content (%) ATF (hr) 0.83 16.4 48 48 Remark Control

Example 3

The procedure of Example 1 was repeated except the testing method was replaced by the following method.

Four coated cups were tested by the following method: 1) Oil fried pre-shaped cup noodles, such as those available in the market, were placed in each cup. 2) Three grams of red pepper powder were spread evenly onto the noodle surfaces. 3) Each cup was tightly sealed with an adhesive label and plastic stretch film, and placed in the oven at a temperature of 149° F. (65° C.). 4) Each sample was checked for stains first every hour during a 7 hour period and then once every 8 hours until failure for a total of 72 hours or 3 days.

The average time to failure (ATF) was calculated similar to that set forth in Example 1. The maximum ATF value of 72 hours represents that none of the cups for the cup group sampling exhibited any stain or leakage. The minimum ATF value of 1 hour represents that all of the cups in the cup group sampling failed within the first 1 hour.

The results for the stain resistance, in terms of ATF, are shown in Table 3. TABLE 3 Coating rate (mg/cm²) 0 3.8 ATF (hour) 1.8 72.0 Remark Control

As indicated in Table 3, the cups with the latex coating had an increased ATF for the mixture of fried noodles and red pepper powder compared to the cups without the latex coating (control).

Example 4

The procedure of Example 1 was repeated except the testing method was replaced by the following method.

The coated cups were tested by the following method: Salsa sauce, which is a spicy sauce, was poured at room temperature into each container to fill the cup up to about 90% of its capacity. The outer surface of each container was observed for stains and leakage every one hour for a total of 48 hours.

The average time to failure (ATF) for each cup group sampling was calculated by adding the time to failure for each container, and dividing the total time to failure by the number of containers tested. Typically, five cups in each group were tested. A maximum ATF value of 48 hours means that none of the cups in that group exhibited any stain or leakage. A minimum ATF value of 1 hour means that all of the cups in that group failed within the first hour.

The results for the stain resistance, in terms of ATF, are shown in Table 4. TABLE 4 Coating rate (mg/cm²) 0 3.8 ATF (hour) 2.0 48.0 Remark Control

As indicated in Table 4, the cups with the latex coating had an increased ATF for salsa sauce compared to the cups without the latex coating (control).

While the present invention has been particularly set forth in terms of specific embodiments thereof, it will be evident to those skilled in the art that numerous variations and details of the invention may be made without departing from the instant invention as defined in the appended claims. For instance, different types of latex coatings can be applied in one or more layers to one or more surfaces of the container. 

1. A molded thermoplastic container for retaining liquid and food substances and having inner and outer surfaces, comprising: a latex coating applied to at least a portion of at least one of said inner and outer surfaces of said molded thermoplastic container for coating said container.
 2. The molded thermoplastic container of claim 1 wherein said molded thermoplastic container is made from expandable thermoplastic particles.
 3. The molded thermoplastic container of claim 2 wherein said expandable thermoplastic particles are expandable polystyrene particles.
 4. The molded thermoplastic container of claim 1 wherein said latex coating is comprised of a monomer selected from the group consisting of butadiene, n-butyl acrylate, i-butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, octyl acrylate, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl pivalate, vinyl neo-decanoate, acrylonitrile, methyl acrylonitrile, acrylamide, styrene, α-methyl styrene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate.
 5. The molded thermoplastic container of claim 4 wherein said latex coating is comprised of a polymer selected from the group consisting of a homopolymer, a copolymer of two or more of said monomers, and a copolymer of two or more of said monomers with the following functional monomers including acrylic acid, methacrylic acid, itaconic acid, fumaric acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, acrylamide, dimethyl meta-isopropenyl benzyl isocyanate, N-methylolacrylamide, N-methylol methacrylamide, N-(iso-butoxymethyl)acrylamide, glycidyl acrylate, glycidyl methacrylate, sodium styrene sulfonate.
 6. The molded thermoplastic container of claim 1 wherein said latex coating is comprised of a polymer selected from the group consisting of acrylate, ethyl acrylate, methyl methacrylate, methacrylate, acrylic acid, methacrylic acid, and monomers or copolymers of said monomers combined with vinyl acetate or styrene.
 7. The molded thermoplastic container of claim 1 wherein said latex coating is selected from the group consisting of latex of methyl methacrylate and styrene copolymer, latex of methyl acrylate and styrene copolymer, latex of acrylic acid and styrene copolymer, and latex of butadiene and styrene copolymer.
 8. The molded thermoplastic container of claim 7 wherein said latex coating is latex of methyl acrylate and styrene copolymer.
 9. The molded thermoplastic container of claim 1 wherein said latex coating has a thickness ranging from about 0.10 mils to about 5.0 mils.
 10. The molded thermoplastic container of claim 1 wherein said latex coating is applied to said surfaces of said container via a spraying process, and wherein said latex coating when diluted has a solids content ranging from about 40% to about 47% by weight.
 11. The molded thermoplastic container of claim 1 wherein said latex coating is applied to said surfaces of said container via a dipping process, and wherein said latex coating when diluted has a solids content ranging from about 8% to about 20% by weight.
 12. The molded thermoplastic container of claim 1 wherein said latex coating is applied to said surfaces of said container via a brushing process, and wherein said latex coating when diluted has a solids content ranging from about 40% to about 47% by weight.
 13. The molded thermoplastic container of claim 1 wherein said latex coating is comprised of a solids phase and a water phase, and wherein said solids phase is about 50% by weight based on the weight of the latex coating.
 14. A method for forming a container for retaining liquid and food substances, the steps comprising: forming a molded thermoplastic container having an inner surface and an outer surface, and applying a latex coating to at least a portion of at least one of said inner surface and said outer surface of said container for making said container leakage and/or stain resistant to said liquid and food substances.
 15. The method of claim 14 the steps further comprising: applying said latex coating to said inner surface of said container.
 16. The method of claim 14 the steps further comprising: applying said latex coating to said outer surface of said container.
 17. The method of claim 14 wherein said latex coating is selected from the group consisting of latex of methyl methacrylate and styrene copolymer, latex of methyl acrylate and styrene copolymer, latex of acrylic acid and styrene copolymer, and latex of butadiene and styrene copolymer.
 18. The method of claim 14 wherein said latex coating is latex of methyl acrylate and styrene copolymer.
 19. The method of claim 14 wherein said latex coating is applied to said container via a spraying process.
 20. The method of claim 14 wherein said latex coating is applied to said container via a dipping process.
 21. The method of claim 14 wherein said latex coating is applied to said container via a brushing process.
 22. An article of manufacture having improved storage longevity, improved stain resistance, and/or improved leakage resistance, comprising: a molded thermoplastic container coated with a latex coating and containing a liquid substance or a food substance.
 23. An article of manufacture of claim 22 wherein said container has improved stain resistance.
 24. An improved method for storing liquid and food substances by using the container of claim
 1. 